This invention relates generally to development of dry toner images wherein the resultant image on a recording sheet exhibits low toner pile height.
A typical electrostatographic printing machine (such as a photocopier, laser printer, facsimile machine or the like) employs an imaging member that is exposed to an image to be printed. Exposure of the imaging member records an electrostatic latent image on it corresponding to the informational areas contained within the image to be printed. The latent image is developed by bringing a developer material into contact therewith. The developed image recorded on the photoconductive member is transferred to a support material such as paper either directly or via an intermediate transport member. The developed image on the support material is generally subjected to heat and/or pressure to permanently fuse it thereto.
Modern electronic printers are capable of producing quite complex and interesting page images. The pages may include text, graphics, and scanned or computer-generated images. The image of a page is described as a collection of simple image components or primitives (characters, lines, bitmaps, colors). Complex pages can then be built by specifying a large number of the basic image primitives. This is done by a page description language such as PostScript. The job of the electronic printer's software is to receive, interpret and draw each of the imaging primitives for the page. The drawing or pasteurization must be done on an internal, electronic model of the page. This electronic model of the page is often constructed in a data structure called an image buffer. The data contained is in the form of an array of color values called pixels. Each pixel corresponds to a spot, which can be marked on the actual page, and the pixel's value gives the color that should be used when marking. The pixels are organized to reflect the geometric relation of their corresponding spots. They are usually ordered such as to provide easy access in the raster pattern required for marking.
Two types of developer materials are typically employed in electrostatographic printing machines. One type of developer material is known as a dry developer material and comprises toner particles or carrier granules having toner particles adhering triboelectrically thereto. Another type of developer material is a liquid developer material comprising a liquid carrier or dispersant having toner particles dispersed therein.
Development with liquid developers in full color imaging processes has many advantages, such as a texturally attractive print because there is substantially no toner height build-up, whereas full color images developed with dry toners often exhibit height build-up of the image where color areas overlap. Further, full color prints made with liquid developers can be made to have either a uniformly glossy or a uniformly matte finish, whereas uniformity of finish is difficult to achieve with powder toners because of variations in the toner pile height.
High toner pile height is a major document appearance problem for powder xerography. It is obvious to the customer not only as increased document thickness but also in other undesirable ways, such as paper curl. In addition to being an aesthetic dissatisfier, paper distortion due to curl and ripple increases the jam rate and complicates paper handling and document finishing. This is objectionable in any market, but especially in the production color printing market, which demands high-speed reliable operation and is accustomed to the look and feel of lithography.
A need exists for an electrophotographic printing machine that can produce texturally attractive color prints with substantially no height build-up employing dry developers. A simple, relatively inexpensive, and accurate approach to produce color prints in such printing systems has been a goal in the design, manufacture and use of electrophotographic printers. The need to provide accurate and inexpensive color reproduction with dry developers has become more acute, as the demand for high quality, relatively inexpensive color images and the machines that produce them have increased.
There has been provided a method to form a seven-color (CMYKRGB: cyan, magenta, yellow, black, red, green, blue) or eight-color (CMYKRGBW: cyan, magenta, yellow, black, red, green, blue, white) having reduced toner pile height than in four-color xerography, resulting in more uniform image gloss. The method includes the steps of: forming first spot next to spot toner images by placing spots of toner of a first color next to spots of toner of a second color on a first photoconductive member; forming second spot next to spot toner images by placing spots of toner of a third color next to spots of toner of a four color on a second photoconductive member, and transferring said first and second spot next to spot images to form a composite spot next to spot image on an intermediate imaging member.